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Re^2: I don't understand a piece of Perl/Tk code

by spx2 (Deacon)
on Aug 17, 2007 at 08:36 UTC ( [id://633245]=note: print w/replies, xml ) Need Help??


in reply to Re: I don't understand a piece of Perl/Tk code
in thread I don't understand a piece of Perl/Tk code

Hi! Very nice piece of code. Altough i still have questions regarding it. In particular,you apply method move to $canvas altough you want to move $dragster. There is a hint about this in the fact that move() method has a parameter called "current",is this indicating that $dragster is the current object that has focus or... ?

Now i have a second question. Is there first parameter in bind user-defined ,or is it from some list of possible values ? is the first argument to bind('move') in any way linked to the method move wich is applied to canvas ?

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Re^3: I don't understand a piece of Perl/Tk code
by zentara (Archbishop) on Aug 17, 2007 at 12:42 UTC
    You need to understand how the canvas tag system works. The dragster IS NOT an object, so it cannot have methods. I could make it into object, with some package code, but in general, "items" on a canvas, are elements of the canvas widget.

    Your second question is about canvas tags also. There is a difference between the canvas's bind and the normal Tk::bind. The canvas's bind will let you bind to a tag. If you look at each canvas item's creation, you will see it is given a tag(s). This is the basis of the canvas's power, because you can do all sorts of trickery with addtag and deltag to change an item's tags dynamically. So you can do things like setup a callback when a mouse enters any item with a certain tag. Like this:

    #!/usr/bin/perl use Tk; my $mw = MainWindow->new(); $mw->geometry("600x400+100+100"); $canvas = $mw->Canvas(width => 600, height => 400)->pack(); $canvas->Tk::bind("<Button-1>", [ \&print_xy, Ev('x'), Ev('y') ]); # This draws half of an oval $oval = $canvas->createOval(100,100,200,250,-fill => 'white',-tags => +"blue"); $canvas->Tk::bind("<Button-3>", sub {$canvas->itemconfigure($oval,-fil +l => "red")}); $canvas->bind('blue', '<Enter>', sub { $canvas->itemconfigure("blue", -fill => "blue"); } ) +; # sub {exit}); # When the mouse is not over, color it black. $canvas->bind("blue", "<Leave>", sub { $canvas->itemconfigure("blue", -fill => "black"); }); #$tw->tagBind('tag','<Enter>',sub{$overtag=1}); MainLoop; sub print_xy { print "@_\n"; my ($canv, $x, $y) = @_; print "(x,y) = ", $canv->canvasx($x), ", ", $canv->canvasy($y), "\n" +; }

    I'm not really a human, but I play one on earth. Cogito ergo sum a bum

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